1. Field of the Invention
The invention relates in general to a method for evaluating the number of used fee units of a card owner which are stored on credit cards for automatic vendors and of a central evaluation location particularly for telecommuication equipment connected to a switching center such that the credit cards are provided with personal identification features such as a personal identification number.
2. Description of the Prior Art
A credit card is known for frequent callers in telecommunication technology wherein calls may be made from public telephone booths and can be charged to the home telephone number. The accounting procedure therefore sequences in the following manner. The public card telephones are connected to an accumulator (concentrator) to which the card sends a number of a subscriber as well as the number of fee units which have already been used by telephoning with the particular card. This does not occur after every telephone call because individual accounting entries would be too expensive. Only when the number of units used are in the range of 40 through 50 does the card automatically emit the unit number to the accumulator or concentrator. For 40 components of telephone fees, thus only one component gives rise to accounting fees.
This manner of accounting however, has the disadvantage in that credit cards can be manipulated or changed because if the card owner understands the system, he can simulate a debiting to the central evaluation location which has not yet been carried out by performing operations on the credit card.